US President Barack Obama on Wednesday raised the plight of the imprisoned Liu
Xiaobo, his successor as Nobel peace laureate, directly with President Hu
Jintao of China, an official said.

"The president did raise Liu's case," the senior US official said on condition of anonymity, adding that Mr Obama reiterated his belief that all freedom of expression was a universal right.

Mr Obama has repeatedly called on China to free Mr Liu, calling him an "eloquent and courageous spokesman for the advance of universal values through peaceful and non-violent means".

The official declined to characterise Mr Hu's response to Mr Obama's comments, made during the Chinese president's state visit to the United States.

Mr Liu, a writer and one-time professor, was sentenced to 11 years in prison in 2009 on subversion charges after co-authoring Charter 08, a bold petition calling for political reform in one-party Communist-ruled China.